The invention relates to a system for transfer of data and/or electric current for a steerable horizontal boring machine for laying and destructive replacement of supply lines.
Such systems are used in the trenchless laying of supply lines, for example for transfer of measuring data from a measuring instrument located in the drill head to an external data utilising unit. The transfer usually takes place via a radio connection, as described in German patent specification 44 38 934. For this purpose in known devices inclination sensors, roll sensors and temperature detectors are fitted in the drill head, the signals from which are utilised outside the underground bore. Particular importance attaches to the determination by means of a locating transmitter of the position of the steerable drill head as it progresses underground.
All the sensors and other consumers of electricity require a current supply which is provided by accumulators fitted in the drill head or through an electric cable leading to an external power supply. Accumulators have the disadvantage of only being usable for a limited period of time, which can give rise to considerable problems if the transmitter fails during a boring operation because the accumulator is flat and the drill head can no longer be located.
The supply of current through a cable, as known from German Offenlegungsschrift 196 13 788, avoids the problem of time-limited utility. In this device a measuring instrument for measuring the tensile force between an expanding head and a pipe that is being pulled in is connected by a cable running parallel to the pipe being pulled in or to the drill string to a control box located on the surface of the ground.
In German Utility Model specification 88 09 108 an elongated body to be driven into the ground is described in which the electrical supply lines run in the pipe jacket. Rotation of the pipe must be avoided in order to avoid twisting the cable.
In all cases of connection by cable there is the problem that the boring machine is driven into the ground one element at a time by means of lengths of rod or lengths of pipe. This necessitates stepwise connection of the elements, and thus also of the lengths of cable. The respective points of connection can be subjected to harmful axial loads, particularly in the case of percussive boring, while in the case of rotary boring twisting of the cable must be avoided.
The object of the invention is to provide a system for transfer of signals or electric current for a steerable horizontal boring machine which avoids the above-mentioned disadvantages and permits reliable and problem-free use of a cable connection between a consumer or sensor and a source of current or a data utilising unit.
To achieve this object, the invention provides a system comprising various adapters as set forth in the independent claims herein. The system or the adapters is or are suitable both for percussive and for rotary boring operations, and preferably comprise three elements (drive adapter, rod adapter, consumer adapter) for connection of the cable line.
The signal transfer between the rotatable string and data utilising unit or between a power source and the rotatable string can be effected by means of a drive adapter having connecting means which are stationary relative to the string. It is particularly advantageous if a slip ring connection includes an axially slidable slip ring and/or current collector, in order to neutralise axial accelerations of the drill string such as may occur when drilling in hard rock or when using a striking mechanism, and thus prevent damage to the slip ring connection.
In the case of rotary operation of the boring machine the drill string rotates, and with it the slip ring fitted on the string and the cable inside the string. The current collector connected to the power source and/or to the data utilising unit is in contact with the slip ring, but does not transmit any rotary movement, since it is fixed on the drive side. Twisting of the cable is thus ruled out.
The individual lengths of the string can include internal electric leads with string adapters for connection of the leads, which can be automatically connected, together with the string lengths, by having the ends of the leads fixed in the string head and aligned so that making a connection between two string lengths also results in connection of the ends of the leads.
The cable can run axially in the drill string length and emerge centrally from the string head.
The electrical connections, especially the connection between the consumer located in the boring machine and the cable, can include connecting elements (consumer adapters) which permit relative axial movement between the connected elements without transmission of axial forces. This connection of cable elements or of electrical consumer and a cable element makes problem-free use of the boring machine in hard rock or with percussion drive possible without putting a strain on the electrical connection. In this way, together with damping of the transmitter or sensor by means of suitable damping elements in the sensor housing, an optimum transfer system for rotary and percussive boring operation is provided.